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914World.com _ 914World Garage _ Transaxle trouble
Posted by: Hank914 Nov 3 2014, 12:17 AM
I earlier added to the "what you did today thread" but I thought I would start a new thread with some more details on my transaxle troubles.
So I recently installed by rebuilt tranny after the PNW tranny clinic. I also converted from tail to side shift, and all the bushings. The previous owner (40 yrs) rebuilt the engine after 97k miles in 2007, but afaik did nothing on the tranny. The bushings were shot. Last weekend, after logging 120 test miles around Central Oregon, I thought I'd take her down to the Bay Area. About 130 miles into the trip, I hear a loud bang and spin a 360 into the ditch. During the fun, I figured I had a blowout. But not tire problems just a locked up rear differential.
I pulled the tranny and this is what I saw. (Please excuse the large photos, but it adds detail)
So I opened up the tranny case and found some interesting stuff.
Pictures to follow...
Posted by: Hank914 Nov 3 2014, 12:23 AM
Here are some more pictures of the damage...
Looks fine on that side...
But not so much on this picture.
Posted by: Hank914 Nov 3 2014, 12:29 AM
Here are a couple more pics...
And a close up...
Posted by: Hank914 Nov 3 2014, 12:33 AM
So, any ideas on...
1). 
made that piece decide to come off?
I was in 5th gear doing about 65mph. I use this car (1.7L) as a commuter. I don't push it very hard at all. I did switch to Fuchs 4 lugs with 205's instead of the 165's the PO had on it.
2). How often does this happen?
3). Why does this happen?
Any other thoughts?
Thanks.
Posted by: Dave_Darling Nov 3 2014, 01:20 PM
2) Not very often!
3) In very high-torque applications, galling develops on the pinion teeth. After some time, it gets bad enough that the teeth start to shear off.
I'm pretty sure that's not what happened here.
Could the pinion shaft bearings be loose enough that the pinion was not held engaged properly to the ring gear? Any foreign objects in the trans? Anything that looks like it might have come adrift from somewhere else and gotten jammed into the R&P mesh?
That trans case is.... scary.
--DD
Posted by: chads74 Nov 4 2014, 07:57 AM
I had the transmission on my high school 914 lock up and send me into a ditch also. Just pulled it and sent off for a rebuild, I never found out what the cause was. Hopefully you came out injury free, besides maybe some new undies.
Posted by: 6freak Nov 4 2014, 09:01 AM
PNW tranny clinic 
...theres always someone with an issue`s after one of these clinics, 
your the someone this time ..thats sucks IMO the lash was not set proper on the R&P.. .I have a case in Tacoma if ya need one? just come get it good luck
Posted by: Dr Evil Nov 5 2014, 08:11 AM
Not sure what 6freak is talking about, but to address your qustions.
This is not common. I have seen one come to me to be repaired out of over 300 I have had my hands in. A few things to note regarding yours:
You have new bearings and they were fitted just fine. You did not have any galling on your pinion, this was inspected at time of rebuild and I had parts on hand to swap if there was. This is most likely due to metal fatigue from 40yrs of use, but I can not be sure. Pinion was not reset and did not need it. It would need to be way out to be the cause of that.
It would appear that the guts are in good shape for the most part, and we can work with that.
One possibility is that with the rebuild there was a change in how stresses in the transmission were communicated to the parts and it found the weakest spot. However, I am speculating.
I'll help you get this sorted out with as little pain as possible.
Posted by: 396 Nov 5 2014, 08:53 AM
Here are a couple more pics...
And a close up...
I'm no expert but a simple logical person
.If it was me, I would simply start with a new core trans.. Trying to reuse most of the parts one would have to really inspect and make sure there no metal wedge between the gears. Once that happens, the gears will never mesh 100%. Thus why take a chance. Then it's just me...do it right once ...and don't Mickey Mouse it for the long term. Good luck
Posted by: jkb944t Nov 5 2014, 12:05 PM
I don’t see any gulling of the remaining section of the pinion so it wasn’t a setup issue.
It was either an inherent defect in the gear that was there from manufacturing that unfortunately decided to give out now or something foreign was floating inside the transmission and locked up in between the pinion gear teeth.
Jeff B
Posted by: Hank914 Nov 5 2014, 01:12 PM
I don’t see any gulling of the remaining section of the pinion so it wasn’t a setup issue.
It was either an inherent defect in the gear that was there from manufacturing that unfortunately decided to give out now or something foreign was floating inside the transmission and locked up in between the pinion gear teeth.
Jeff B
I looked pretty closely to see if there was any foreign floater object that I could identify as the reason. I found nothing but smaller bits of metallic shrapnel and the one larger "tooth" that broke off. Hence I think it is an inherent defect from the beginning.
And that's why I started this tread. How often? Sounds like 'not very' is the consensus answer.
Posted by: Dr Evil Nov 5 2014, 02:42 PM
I am wondering what the diff guts look like. There is a possibility that the diff seized and that cause the pinion to lose a tooth. I would need all the parts here to do a post mortem.
Posted by: Jonathan Livesay Nov 5 2014, 02:52 PM
I am wondering what the diff guts look like. There is a possibility that the diff seized and that cause the pinion to lose a tooth. I would need all the parts here to do a post mortem.
I broke the diff ring gear on a 944S that I used to own and it cracked the case just like that.
Posted by: jkb944t Nov 6 2014, 12:03 PM
I am wondering what the diff guts look like. There is a possibility that the diff seized and that cause the pinion to lose a tooth. I would need all the parts here to do a post mortem.
A locked diff does seem to be a very good possibility and would explain the crack in the side of the case.
Jeff B
Posted by: Tbrown4x4 Nov 6 2014, 02:00 PM
Did you experience any tire slip and then regain traction suddenly? That could transmit the kind of shock load that could damage the pinion. How did the ring gear look?
Posted by: nine9three Nov 6 2014, 03:26 PM
That seal looks really high. Was it like that before the damage?
Posted by: Hank914 Nov 6 2014, 05:14 PM
Did you experience any tire slip and then regain traction suddenly? That could transmit the kind of shock load that could damage the pinion. How did the ring gear look?
After the loud bang, both rear tires locked solid. Laid two solid black stripes on the pavement. Never regained traction. I'll see if I can take some detailed picks of the diff. I'm sending it off to the DrEvil for a post mortum.
Posted by: Tbrown4x4 Nov 6 2014, 06:11 PM
Well, I'll be following this with great interest.
I assume you were towed home. You never mentioned if the tires were still locked up when it was put on the flatbed.
What seems really strange to me is the torque applied to the ring and pinion should be at its lowest in 5th gear. Just the opposite of a hard launch in 1st.
(Like when my kid brother was popping wheelies in my Corvair powered sand rail. Lots of little pieces came out of the drain plug that day!)
Posted by: Dr Evil Nov 6 2014, 09:52 PM
That seal is high. Not out of tolerance, but not where I like it. I wonder if it was pushed out as I would not have let that seal pass inspection.
Posted by: 6freak Nov 7 2014, 08:50 AM
Not sure what 6freak is talking about,
just saying with the party type atmosphere
it could be easy to miss details.. your still at 99.5% to the good 
if its man made it can break,even when new
Posted by: Dr Evil Nov 7 2014, 09:00 AM
Well, I was not drunk at this clinic and I am not sure what you are insinuating that I missed at the one at your house, and I take accusations like that seriously. All I have with my biz is my reputation. So, what exactly are you referring to?
And, your assessment that the pinion depth was off is way wrong. Pinion is set finite for noise reasons. It will work just fine if out by an amount that is not ridiculous. If it were out, he would have heard loud whining during the long trial that he did. Your assumption seems to have missed some very key details that were provided.
Posted by: Hank914 Nov 7 2014, 09:28 AM
Well, I'll be following this with great interest.
I assume you were towed home. You never mentioned if the tires were still locked up when it was put on the flatbed.
What seems really strange to me is the torque applied to the ring and pinion should be at its lowest in 5th gear. Just the opposite of a hard launch in 1st.
(Like when my kid brother was popping wheelies in my Corvair powered sand rail. Lots of little pieces came out of the drain plug that day!)
Tires were locked solid on the road. In the gravel ditch. And on the flatbed tow truck. Tow driver was very careful during the load as he is a porsche oldie fan and did not want to damage the diff/transmission. (Lol). He loaded it rear first by putting the bed about 6 inches from the tires, then dragging the car and tires (still locked) onto the start of the flatbed and then added plastic shims under the tires to allow them to slide on the bed as it was pulled to the middle of the flatbed deck. Same during the unload. I then jacked the rear end up and slipped wheel dollies under the rear wheels to move it into the garage to remove the tranny. The tires were locked until I pulled the tranny out.
And I agree about the torque in 5th being lowest. And little pieces were left in the case. I just did not see any big foreign objects to be named the offender. I might have missed it.. Or it might have disintegrated. Interesting that the "tooth" came off so clean and so large. Almost like I used a chisel. And it fits back on clean ad well. Maybe super glue it back?
Posted by: Dr Evil Nov 7 2014, 09:32 AM
Whats the diff look like? A sheared roll pin at the block in the center of the diff would cause a grenade like this.
Posted by: Hank914 Nov 7 2014, 09:39 AM
Well, I was not drunk at this clinic and I am not sure what you are insinuating that I missed at the one at your house, and I take accusations like that seriously. All I have with my biz is my reputation. So, what exactly are you referring to?
And, your assessment that the pinion depth was off is way wrong. Pinion is set finite for noise reasons. It will work just fine if out by an amount that is not ridiculous. If it were out, he would have heard loud whining during the long trial that he did. Your assumption seems to have missed some very key details that were provided.
Not only me, but the Porsche mechanic I had check it out after I drove around for about 100 miles. He heard nothing from the tranny. What he did find was the cause of the intermittent rattle around the fan. I took off the hose clamps to the heater hoses and left one behind. He pulled it from the fan area before it did anything major. But he tested the tranny shifting, checked the linkage and bushings, and did an overall sanity check. Said the tranny sounded fine, but of course did not pull the tranny and open it up. FWIW
Posted by: Hank914 Nov 7 2014, 09:42 AM
Whats the diff look like? A sheared roll pin at the block in the center of the diff would cause a grenade like this.
I'm back so I can take some close up photos in a few hours. If I can't get the bearing chases out, I may send you the whole case as well, to do a complete post mortum. That way you can see the diff as well. Or not?
Posted by: Dr Evil Nov 7 2014, 09:48 AM
Nah, save the money on shipping unless you really want me to mess with it. If the races give you a hard time, then send it to me and I will handle the whole shooting match. Pics of the diff and associated gears should suffice, though
Posted by: rhodyguy Nov 7 2014, 09:55 AM
The recent colonic was nothing was nothing like the one held in tacoma. I was there until midnight and I didn't note any consumption of alcohol until nearly everyone cleared out. Much like a beer after work. There was plenty of beer in the coolers and a box full of hard alcohol that went untouched. No snow mobiles raising hell and disturbing the neighbors during the middle of the night either. If you catch my meaning and you get my drift....10 bonus points for fans of Firesign theater that know what that came from.
Posted by: Mr.242 Nov 7 2014, 10:07 AM
Take a 40 year old transmission. Rebuild it to new spec. Tolerances become tighter than a 'vaginal rejuvenation'.
Facts: both rear wheels locked. Means the diff did not spin. Lock rear wheels caused the spin.
The cracked housing is the result of the torque (energy) goes some somewhere and produces 'work'. That work cracked the cases. It wasn't the case breaking and then wheels locked. Also the energy could have snapped the pinion too. Engine energy is twisting it as the diff quits spinning suddenly.
Autopsy will determine why the diff quit rotating and in such a way it stopped both sides.
Yo 6Freak!!! As for the 'party' insinuation; You're certainly making a huge jump of speculation. The clinic I did i Shelton was all business. I seen some of the hardest working wrenches. There was no one partaking and the 'party' didn't happen as lodging wasn't so easy. A few beverages to wet the whistle but far from impairing anyone from properly rebuilding.
What was the motivation in saying any such garbage? Or slander? Next you'll say it's because we didn't use protection as we screwed off and clearly the tranny caught an STD! Whiskey Tango Foxtrot, over!?
Posted by: Hank914 Nov 7 2014, 10:18 AM
Take a 40 year old transmission. Rebuild it to new spec. Tolerances become tighter than a 'vaginal rejuvenation'.
Facts: both rear wheels locked. Means the diff did not spin. Lock rear wheels caused the spin.
The cracked housing is the result of the torque (energy) goes some somewhere and produces 'work'. That work cracked the cases. It wasn't the case breaking and then wheels locked. Also the energy could have snapped the pinion too. Engine energy is twisting it as the diff quits spinning suddenly.
Autopsy will determine why the diff quit rotating and in such a way it stopped both sides.
Yo 6Freak!!! As for the 'party' insinuation; You're certainly making a huge jump of speculation. The clinic I did i Shelton was all business. I seen some of the hardest working wrenches. There was no one partaking and the 'party' didn't happen as lodging wasn't so easy. A few beverages to wet the whistle but far from impairing anyone from properly rebuilding.
What was the motivation in saying any such garbage? Or slander? Next you'll say it's because we didn't use protection as we screwed off and clearly the tranny caught an STD! Whiskey Tango Foxtrot, over!?
Probably yanking somebody's chain.
But if he's serious, then I'll add this tidbit. My tranny was "buttoned up" on Sunday late morning, not Sat night. No brewskies, just coffee and donuts.Posted by: Dave_Darling Nov 7 2014, 10:54 AM
Well, that's your problem right there! Everybody knows that the secret formula for super glue is powdered sugar and gear oil!!
--DD
Posted by: veekry9 Nov 7 2014, 12:40 PM
https://www.google.ca/#q=fatigue++cracks+in+gears
https://www.google.ca/search?biw=1440&bih=712&source=lnms&tbm=isch&sa=X&ei=RA5dVKasEMuTyAT_g4GoBA&ved=0CAYQ_AUoAQ&q=fatigue%20cracks%20in%20gears
Classic example of tooth-root crack propagation.
Ask any A+P if a visual inspection is enough.
Magnaflux,X-ray,ultrasonic,penetrant methods are required.
Even then..
Further reading.
The science of why things break.
http://www.kettering.edu/news/contact-fatigue-numbers-0
Keep it super lubed and cooled.
Posted by: Hank914 Nov 7 2014, 04:43 PM
More pics. The big piece is from the pinion.
The small pieces are from the diff. 15 outta 31 teeth shredded. 
Posted by: Hank914 Nov 7 2014, 04:50 PM
The differential. The quarter is for reference only. It was not in the transaxle. 
And now some close ups. 
The quarter is underneath the first (or last?) broken tooth on the diff.
Posted by: Hank914 Nov 7 2014, 04:53 PM
Here is a pic of the quarter next to the other side of the diff, where the teeth broke. 
Posted by: SirAndy Nov 7 2014, 04:53 PM
Posted by: Dr Evil Nov 7 2014, 05:24 PM
How about the guts of the diff? I expect the gear carnage, but the guts may tell us something.
Posted by: Hank914 Nov 7 2014, 05:32 PM
Guts looked clean. Both bearings spin freely. Pics to follow.
Posted by: Steve Nov 7 2014, 05:37 PM
Maybe that quarter caused it!! Just kidding..
Seriously I am also curious what could of caused this.
Posted by: Hank914 Nov 7 2014, 05:43 PM
Pics galore. 
Posted by: Hank914 Nov 7 2014, 05:46 PM
More
Posted by: Hank914 Nov 7 2014, 05:50 PM
Last two
I think this bearing is usable. 
Posted by: Hank914 Nov 7 2014, 05:54 PM
Nah, save the money on shipping unless you really want me to mess with it. If the races give you a hard time, then send it to me and I will handle the whole shooting match. Pics of the diff and associated gears should suffice, though
Got the races out, but on the smaller one I could only get one of the clips out. Do you need both little spring clips?
I'm ready to box it up and ship it out tomorrow. Let me know if you want more pics.
I'll pm you regarding bushings etc.
Posted by: Dr Evil Nov 7 2014, 07:19 PM
No need for any of the clips, just as long as the races come with the stack. I will make sure they are good to go as it would such to toss new bearings if not necessary.
When I was asking or guts, I meant the spider gears and shaft INSIDE of the diff 
Posted by: Dave_Darling Nov 7 2014, 11:37 PM
Are you going to re-use anything from that trans? I'd think that it would be far easier (and cheaper!) to just get a new/used trans to use as a core. With the trashed case and the trashed R&P...
--DD
Posted by: Hank914 Nov 7 2014, 11:59 PM
No need for any of the clips, just as long as the races come with the stack. I will make sure they are good to go as it would such to toss new bearings if not necessary.
When I was asking or guts, I meant the spider gears and shaft INSIDE of the diff
Oh....
Posted by: Hank914 Nov 8 2014, 12:01 AM
No need for any of the clips, just as long as the races come with the stack. I will make sure they are good to go as it would such to toss new bearings if not necessary.
When I was asking or guts, I meant the spider gears and shaft INSIDE of the diff
Oh....
Those all looked fine, spun them around and saw no damage.
Same with the splines.
Posted by: Dr Evil Nov 8 2014, 05:21 AM
Interesting. Such damage done by one tooth from the pinion. I am also surprised that the wheels locked as I have seen race boxes with teeth shorn off (I call them hillbilly gears) when a malfunction allows selection of two gears at once, or there is a missed shift. But, the gears are supposed to be the weak link.
Posted by: 6freak Nov 9 2014, 12:38 AM
Well, I was not drunk at this clinic and I am not sure what you are insinuating that I missed at the one at your house, and I take accusations like that seriously. All I have with my biz is my reputation. So, what exactly are you referring to?
And, your assessment that the pinion depth was off is way wrong. Pinion is set finite for noise reasons. It will work just fine if out by an amount that is not ridiculous. If it were out, he would have heard loud whining during the long trial that he did. Your assumption seems to have missed some very key details that were provided.
I was not laying blame in anyway and never said you were drunk.
, sorry you took it that way.I don`t remember any that came from my house that where not 100% correct or never heard of any issues pop up ! there was one in Oregon something backwards gears,Hell I dont remember
.I`m just going on percentage`s fix 100 and 1 is bound to go south or break or leak or something! that`s all i was saying ..he was just the unlucky one
Posted by: Dr Evil Dec 6 2014, 12:38 AM
Well, I have received and have have had time to go through the guts of the tranz. Interesting things found. Lets start with the main culprit that caused the casualty. The roller bearing in 1sy gear failed and welded the pinion shaft to the gear. Thus, the tranz was always in 1st. You can see where this would be a problem when you select 5th. 
Above of the gear is what the roller bearing should look like. 
The race of the int plate bearing was welded to the washer that goes between first and the bearing. You can see the discoloration on the washer from the heat. 
So, why the hell did this bearing fail? Great question, and a great time for some teaching on a very fine point in rebuilding that I have only come across about 2 times.
The bearing and the inner race should be able to pass through the gear with very little friction (basically none if kept parallel to the gear face). I salvaged the dog teeth off of the old, welded 1st as they were in perfect shape. I installed them on the new 1st and then checked everything for fit. That is when I noticed that when the roller bearing and inner race were pushed through to the side of the gear with the dog teeth, it started to bind and eventually stuck. This was odd. I took the dog teeth off and everything pushed through without effort. So, the teeth likely shrank the ID of the gear by such a slight amount that every thing bound up and failed. I put a different set of teeth on the gear and tried everything again and noted that the roller and inner race moved through the gear with no issues.
So, likely scenario is that the dog teeth were manufactured to poor tolerance, closed the ID of the dog teeth side of the gear by a small amount when installed, caused the roller bearing to bind, which welded everything together, and caused the stack to seize.
The easy lesson; if stuff is sticking, look for a cause.
The only other casualties from this; 5th gear had one tooth with a mark on it so 5th was swapped, and the large pinon roller bearing had wear on the race.
Hopefully folks can learn from this. Always good to share things like this.
Posted by: veekry9 Dec 6 2014, 10:20 AM
Illuminating.
Posted by: rhodyguy Dec 6 2014, 12:44 PM
do you know if one of the new bearing sets were installed? or is the failed bearing not one of the ones included in the set?
Posted by: Dr Evil Dec 6 2014, 04:29 PM
The failed bearing was a needle bearing and not one of the new ones. However, one of the new roller bearing was damaged so has been replaced.
Posted by: veekry9 Dec 6 2014, 05:03 PM
I presume the negative clearance on the synchro ring has a limit.
Did the factory shrink them on?
Pressing them would for sure gall the surface.
SOP for 20Krev spindle tooling is that type.
Liquid nitrogen/Hot oil/induction.
Haven't researched the method used,if at all referenced.
Posted by: Dr Evil Dec 6 2014, 08:22 PM
They are pressed on. No NASA shit here. Pretty simple. Also, the offending teeth set went on easy which is misleading.
Posted by: veekry9 Dec 6 2014, 10:55 PM
SOP in any m/c shop cool the male heat the female.
Since'68,a Bearing worth 30K is given no chance to fail on first run.
Turbine power generators and transmission.
Nothing to it.
Delta T.
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